1. Field of the Invention
The present invention relates to an optical element adjustment structure used, for example, to perform rotational adjustment of a diffraction grating or other optical element. The invention also relates to an optical pickup provided with such an optical element adjustment structure.
2. Description of Related Art
A diffraction grating for splitting light emitted from a light source is sometimes disposed in optical pickup optical systems of the conventional art (see, for example, JP-A-2005-18845 and JP-A-11-110775). Due to the presence of the diffraction grating, it becomes possible to employ, for example, a three-beam method, a differential push-pull (DPP) method, or another method to generate a tracking error signal.
Typically, a diffraction grating is secured to a base (optical stage) of the optical pickup after rotational adjustment has been performed to bring the positions of a plurality of spots of light formed on an optical disk to target positions. In some cases, diffraction gratings are formed of resin, while in other cases they are formed of glass. Blu-Ray (BD) disks and other optical disks that can record large volumes of information have become commercially viable of late, and currently, most diffraction gratings provided to BD-compatible optical pickups are formed using glass rather than resin.
When formed using glass, the diffraction grating is typically attached to the base of the optical pickup in a state of being held by a holder (optical element holder), and rotational adjustment of the diffraction grating is performed while the holder is caused to rotate. When formed using resin, the diffraction grating is sometimes held in a holder, or at other times is attached to the base of the optical pickup in the form of a single member having both the function of a diffraction grating and the function of a holder.
A conventional art configuration example where a diffraction grating is held in a holder for attachment to the base of an optical pickup will now be described. FIG. 10 is a schematic perspective view showing a diffraction grating prior to attachment to a base in a conventional art optical pickup. FIG. 11 is a schematic perspective view showing a diffraction grating attached to a base in a conventional art optical pickup.
As shown in FIG. 10, in the conventional art optical pickup, a substantially cylindrical holder 102 made of resin is employed as the holder for holding a diffraction grating 101. The diffraction grating 101 is anchored in a substantially center section of the holder 102 using an adhesive or the like. The holder 102 holding the diffraction grating 101 is housed within a hollow, substantially cylindrical housing space 103a provided to a base 103 of the optical pickup.
As shown in FIG. 11, the holder 102 housed within the housing space 103a is pressed against an abutment face 103b of the base 103 by a spring 104 arranged on the back of the holder 102 (see FIG. 10). Specifically, the holder 102 is held in a state of being housed within the housing space 103a through the action of the spring 104. However, as mentioned previously, the diffraction grating 101 must be rotationally adjusted. For this reason, the urging force of the spring 104 is adjusted such that rotational adjustment may be performed with the holder 102 pressing against the abutment face 103b. 
As shown in FIG. 10, an adjustment slot 102a into which an adjustment tool is inserted is formed in the holder 102. As shown in FIGS. 10 and 11, a cutout 103c into which an adjustment tool is inserted is formed in the optical pickup base 103. Accordingly, rotational adjustment of the holder 102 housed within the housing space 103a and pressed against the abutment face 103b by the spring 104 may be performed using the adjustment tool. Once rotational adjustment has been performed using the adjustment tool, the holder 102 is secured to the base 103 using an adhesive or the like so that no movement occurs. Securing the holder 102 using the adhesive or the like completes attachment of the diffraction grating 101 to the base 103.